"A beautiful nightview in the World"
Hakodate is the southern part of Hokkaido. Most travellers go there for watching one of three most beautiful night views in the World besides HK and Napolis. In fact, you may spend good time there more than that.
3+ hours travel on JR train could bring you there from Sapporo. It seems a long journey. For not wasting the time on travelling, you could also visit Noboribetsu, Toya and some other cities which are between the 2 foresaid cities.